Frequency-dependent electroluminescent device



Sept. 10, 1963 H. F. lvEY 3,103,551

FREQUENCY-DEPENDENT ELECTROLUMINESCENT DEVICE FOR PRESENTING COLORED IMAGES Filed Dec. 24, 1956 2 Sheets-Sheet 1 3,103,551 FREQUENCY-DEPENDENT ELECTROLUMINESCENT DEVICE 2 Sheets-Sheet 2 Sept. 10, 1963 F. lvEY FOR PRESENTING COLORED IMAGES Filed Dec. 24, 195e INVENTOR. HENRY F.' VE'Y. BY@ l To vak/55m' mspy w m I m w m H .Wai/n.4.

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United States Patent O 3,103,551 FREQUENCY-DEPENDENT ELECTRULUMINES- CENT DEVICE FOR PRESENTING CLRED IMAGES Henry F. Ivey, Bloomleld, NJ., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Dec. 24, 1956, Ser. No. 630,356 7 Claims. (Cl. 17g-5.4)

This invention relates to electroluminescent devices and methods for operating same and, more particularly, to an electroluminescent device and method wherein two or more signals may be presented simultaneously and in 4dilerent colors on a viewing screen.

Heretofore there has existed the problem of distinguishing Ibetween two different signals which are to be presented simultaneously on a viewing screen, such as a cathode-ray screen. In applications such -as loran, this has been overcome by transmitting pulses, for example, at a slightly different frequency so that one pulse will travel with respect to the other pulse when simultaneously presented on the viewing screen. In such a system, however, all signals which appear on lthe viewing screen are, of course, of the same color. There are other military and non-military applications Where it is desirable to be able to distinguish, by color difference, two yor more signals which are to be presented simultaneously on ta viewing e screen, such as a cathode-ray screen. In addition, color television has been faced with a similar problem in the adoption `and later rejection of the sto-called CBS telei vision system. The features of this CBS color-television system are now very well known yand include `a mechanical rotating color disc `or scanner in front of the receiver, which disc is synchronized with the individual pictures which appear on the raster. As is .Well'knowm when the scanning disc is rotated rapidly and synchronized with the color-corresponding images appearing on the raster, the eye will blend the primary-color components of the scanning disc in such a manner as to present a colored picture. The mechanical features of this rotating scanner p are extremely objectionable, which when coupled with the incompatibility of the 4system for black and white resulted in the adoption of the presently-accepted dotl sequential system of color television.

Various methods have been suggested for eliminating the mechanical scanning arrangement at the receiver, such as providing a plurality of phosphor layers on the cathode-ray tube and synchronizing the energy of the exciting vcathode rays with the color-corresponding scansione of the phosphor. This allows the electrons to penetrate to varying depths to excite different layers of phosphor material to produce dierent colors 'and such systems Iare described in Patents No. 2,704,783 to Sziklai et al. and No. 2,580,073 to Burton. Such systems rare ydiiicul-t to control with regard to` 4the depth of penetration of the electrons into the phosphor layers. 'In other systems, the actual external filters are electrically changed in color in synchronization with the `application of the color-corresponding scansions, as described in Patent No. 2,727,941 to Fulmer. In still other systems, the phosphor material is selected to be excited to different colors by different frequency X-rays, as described in Patent No. 2,728,010 to Hegyi.

It is the general object of this invention to avoid and overcome the foregoing and other diiculties of and objections to prior-art practices by the provision of a nonmechanical screen for reproducing individual signals in different colors for simultaneous presentation.

` It is a further object to provide a system for receiving different signals as Well as :a system for 'transmitting and receiving different signals and simultaneously presenting Patented Sept. l0, 1963 the received signals in preselected different colors directly e on a viewing screen.

The -aforesaid objects of the invention, .and other objects which will become apparent as the :description pro-` ceeds, :are achieved by providing a viewing screen comprising an electroluminescent phosphorfmaterial having contiguous therewith a photoconductive material and a means for `applying electroluminescent-exciting potentials of different frequency across the phosphor and thephotoconductive material. By varying the frequency of electroluminescent excitation, the phosphor materialcan be made to electroluminesce in two or more colors. alternately fand rapidly exposing the photoconductive ma- 'terial to "an excitation signal corresponding to the signals which are to be presented directly on the screen, the electroluminescent phosphor material may be energized to emit light only at that portion of the viewing screen which has -applied thereto the excitation signal. By synchronizing the ,application Iof the different alternating potentials across the phosphor and photoconductive ma- -ter-ial with the application of the excitation signals to the photoconductive material so that the two 'are `simultaneously applied, a `composite signal presentation in two or more colors may be achieved since the image retention of the eye will not 'distinguish the, rapid alternating electroluminescence by which ythe different colored signals are displayed. In addition; `there has been provided a transmitter Iand receiver arrangement utilizing the foregoing system :for presenting multicolored signals or pictures. A method for operating the receiver andreceiver-transmitting arrangement has also 'been` provided. t

IFor =a better understanding of the invention, reference should be had to the accompanying drawings wherein:

FIG. l illustrates in schematic view, a color-television transmitting system;

FIG. 2 illustrates in schematic view, a receiving system for receiving -two or more signals for simultaneous presentation in different colors on a viewing screen;

FIG. 3 illustrates a variable-frequency source of po- Itential;

. FIG. 4 illustrates an `alternative variable-frequency source of potential;

fFIG. 5 is an enlarged view, partly in section, of the screen portion of the cathode-ray tube shown in FIG. 2, illustrating the construction of the electroluminescent cell and photoconductor arrangement;

FIG. 6 is a View corresponding to FIG. 5, but showing an alternative embodiment of the electroluminescent ycell and photoconductor arrangement; i

PIG. 7 is a View Similar to FIG. 5, but showing a fur-` the electroluminescent cell and photoconductor arrange-` ment, as shown in FIG. 4.

The receiver and the screen system, for example, is

adapted for receiving and simultaneously presenting on the same screen, in different colors, two or more different transmitted signals, independent of the intended purpose for such signal presentation. This system,.however, is particularly adapted for color television and in one embodiment of the invention it has been so illustrated and willbe sozdescribed;

With specific reference to the form ofthe invention` primary color lcomponentszcan beNaried, if desired. The scannin'grdisc V1'4ujisdriven vby a motorlSat a speed such that zicker: ink the' vreceiver system will be minimized, such speedsbeingfrom 120lto 180 revolutions per second, for example, inthecase where thescanningfdisc 14 has three individual. color-lter portions.k t

`Thecolor-scannedobjectfield: is projectedby the lens 16- onto. the scanning tube 20, the output of which is fed into a; transmitter. 22', shown in block diagram. The motor; 18'whi'ch drives the scanningdisc 14 is synchronized with the. transmitter 22.so that the successive scansionswhich. arereceived by the tube 20 are converted into atransmitted.'Videosignal having components which correspond to: the successive scansions receivedby the tube 20. With: this.` transmitted video signal are normally transmitted synchronizing pulses which correspond to the revolutions of therdrivingl motorr18, so that the componentsof thefzvideo signalwhichfcorerspond to the` successive color scansionsare transmitted' with the corresponding synchronizing pulses. All of thissystemis well lknown inthe art 4andcit is generally described'in Patent No. 2,304,081 to Goldmarlc.`

FIG. 2 is shown,'. in schematic view, the receiver system whichmaycbe used. to receivel the` video signal.v

which is transmitted by the transmitter system.y In its preferred Aform, the receiver 30, shown in block diagram, reproduces `from said video signal a plurality of successive. indivdual-excitation: voltagesA which correspond to the successive eld scansions which are effected at the transmitter.. These excitation voltages and the synchronizing pulses are fed into a synchronizer 32, shown in block diagram. A' variable.'frequencysonrce of alterv nating. potential 34 isactuated by-l the synchronizer 32 so that its output is impressed across the screen of the cathode-ray tube 36 in synchronization `with the application of the successive individual signal-excitation voltages which -arer applied' to lactuate corresponding cathode-ray scansions of. the face ofgthe cathode-ray tube 36; The receiver and..synchronizer, as well as all but .the face portions of the cathode-'ray tube 36, may be generally similar to the so-called CBS'color-television receiver.

In FIG. 3.is illustrated in schematic form, a variablefrequency source of alternating potential. In the embodiment as: shown, .a rotating' electrical contact 38,l whose rotationis synchronized with the rotation ofy the scanningl disc 14, is used to actuate thev screen todilerent colors, as `explained hereinafter. Oscillator electrical contacts 40, 40'aand140b. are evenly positioned about the periphso that eachoscillator contact connects its respective oscillat'or across the screen. 42 for slightly lessthan one-third of the time. It will thus rbe. seen that-the foregoing system generallycorrespondsto the CBS system except that Wherefarredliilt'er, for'example, is` normally presented in ifront of the naster, the oscillator '1 will" 1be energized through` .contact .40: Where the green lte-r is normally presented infront of t-he raster in the CBS system, the

" ery of the circle described by the rotation of contact 38 f oscillator 2 will be energized through contact 40a, etc. It should be understood that thisfmechanical make-andbreak may lbe replaced by an` electronic switching system, if desired. If it is desired to present a two-color picture where only two Vsignals are to be presented simultaneously in different colors on the viewing screen, it is obvious that one of the oscillators may be eliminated from the circuit shown inv FIG: 3 vand the electrical contacts for these two oscillators modified accordingly.

lIn FIG. 4 is shown an alternative embodimentof the variable-frequency source of alternating potential. This embodiment corresponds-to that shown in FIG. 3 except that a single oscillator is used and the oscillator tuning is varied so that the desired frequencies will be produced. Oscillators. as maybe usedin the foregoing variable-frequencysources vof potentialare well known. An oscillator for a somewhat similar purpose is shown in-fFIG. 7 of the aforementioned-Patent No. 2,727,941 to Fulmer.

In FIG. 5 is shown anzenlargedview, partlyin' section, ofthe screenfor'viewingportion .42 of the cathode-ray tube 36; 'In its simplest for-mgthisscreen portion 42 oomi prises two x boundingA and. spaced'. electrodes 44V andl 46? havingY sandwiched; therebetween' a layer of eld-nespony sive electrolurninescent phosphor material 48 and a ,photoconductive layerltl;`

By way of explanation, electroluminescence was first completely disclosediby G. Destriau in London, Edinburgh, andy Dublin' Philosophical Magazines, series 7,` volume 38, No. 285, pages 700-737 (October 1947),

article tit-led Ther New Phenomenonof Electrophoto-4 `In the phenomenon of. electrolurnines-- cence,v` selected phosphor materials are placed within the luminescence.

inuence lof anzelectric'eld, such: as by sandwiching the phosphor material between two' spaced electrodes and aprplying an alternating potential between these electrodes. The resulting;electric;iieldwhich is created acrossthe electrodes excites thephosphor material-tto luminescence,

and thek phosphor; materials which display this electro- Suchluminescence.` are. 'thus termed.. lieldv responsive. phosphon'materialsfare normally ad-rnixedwith a dielectric material-or'aseparaftelayer of dielectric material isincluded betweenithezelectrodesin order to prevent any arcing thereacross.whichswouldishort out theelectroluminescen-t cell, but .a separate dielectric Amaterial is onlydesirable'and notcrnandatoryv for the cells may beV operated i under somerconditions without any dielectric where` the applied electric eld's asfhigh as l100 kv. per centimeter. Normallythe.spaced/electrodes are parallel, 'but-they need not be, as where graded: lieldi intensities are desired.

In th'exconstruotiontshownirrFIG. 5, thephosphor material 48 isl positioned: adjacent .the outer electrodev 44, which electrode: constitutesfa viewing. face for the screen 42. 'Ihiselectrode44fis transmissive for. the Vradiationswhich the field-responsive phosphor is capable of gen eratingv when excited-tozluminescence. As a specific'example, the electrode 44 maybe; formed of an electricallyconductive and light-transrnissive layer of tin oxide, which layer may'beapplied onto'a glass foundation platey by' means such as .described in Patent No. 2,522,531 to taneously in blue and green colors, for example, fthephos-H phor may bezinc. sulphide activated by copper and may be prepared by mixing' 100 rnoles of Zinc sulphide with 1 mole ofcoppernitrate and- 0225 mole of zinc chloride, which' adrnixed material maybe firedv in closed silica tubes at about 950"` C. foraboutonehour.y This phosphor will electroluminesce in the green region of the visible spectrum.

when excitedby' a field'havingv a frequency'of 720`cycles,

for example. When excited by a field of a frequency of Y kos., for example, the phosphor will respond in the blue region of the visible speotnlm. `Other two-color phosphors are also available and zinc sulphide which is activated by copper and manganese will respond in the yellow region of the visible spectrum to a eld having a frequency of 720 cycles and in the green region of the visible spectrum to a field having a frequency of 10 kcs. If the two different signals are desired to be presented simultaneously in red and green, for example, two different phosphors can be mixed. For example, greenemitting zinc sulphide, copper-activated phosphor which is coactivated with chlorine may be admixed with a redemitting phosphor such as zinc selenide, activated with copper and coactivated with chlorine. At 720 cycles excitation frequency, for example, this admixture `will respond in `the green region of the visible spectrum and at 10 kcs.` excitation frequency, for example, this admixed phosphor will respond in the red region of the visible spectrum. Such a phosphor admixture is disclosed in copending application of Willi Lehmann, SN. 630,355, titled Electroluminescent Cell, filed concurrently herewith, and owned bythe present assignee, now abandoned. Of course, in all `of the foregoing phosphor embodiments,

fthe exciting oscillators as shown in FIG. 3 should be selected so as to produce the desired frequency.

A three-color phosphor is described in co-pending application of Willi LehmannS.N. 630,040, titled Phosphor, filed concurrently herewith, and owned by the assignee of the present application, nosv Patent No. 2,937,150. Such aphosphor may be prepared by admixing 100 grams zinc sulphide, 1.2 grams manganous acetate, 0.5 grain copper sulphate and 1.5 grams Zinc chloride. Thus this phosphor is Zinc sulphide, activated by r copper and manganese and coactivated with chlorine. The

foregoing admixture may be red in an atmosphere of sulphur vapor for about 1 hour at about 1l00 C., after which the phosphor is reg-round` and washed in potassium cyanide solution. This phosphor electroluminesces in the yellow regions of the visible spectrum at lower frequencies (360 cycles, for example), in the green at about 1 kc., and in the blue at about 30 kcs. and higher. Thus this phosphor may be used where different signals are to be presented simultaneously to the viewer in green, blue and yellow colors. vOther possible variations for varying the colors in which three signals are to be presented simultaneously will be considered hereinafter.

The term photoconductive has been used herein to describe a material whose impedance is decreased or lowered when excited by or irradiated with light or even particle bombardment, such as electrons. The term electron-bombardment-conductive" is normally used to describe materials whose impedance is lowered when excited by electrons. It is thus clear that the term photoconductive as used herein is `generic to both radiation- `induced conductivity and particle-bombamdment-induced conductivity. In addition, the impedance of these photoconductivematerials normally decreases with increased excitation, las is well known. Regarding the term light, it is sometimes given a narrow meaning which refers to electromagnetic energy in the visible spectrum. In a broader sense, however, the term light may be used to include X-rays, ultra-violet light, visible light and infrared light and it is the broader meaning of this `term which is used herein.

The layer of photoconductive material 50 and contiguous layer of phosphor material 48 bounded by electrodes has been previously described in many publications and is described in Patent No. 2,650,310 to White, for example. Such a 'device may be used for a light amplifier and the signals which are to be presented simultaneously in different coloris may actually be amplified, if desired, as hereinafter explained. In the operation of these photoconductive :and electroluminescent devices, a field is applied across the yentire phosphor and photoconductive layer. When the photoconductive layer is not energized, it has a very high impedance and most of the applied electric field will occur across this photoconductive layer with a relatively small electric field appearing across the separate phosphor layer. When the photoconductive layer 50 is energized, as by exciting this layer 50' -with cathode rays, for example, its impedance will drop and the most of lthe applied `electric field will manifest itself across `the phosphor layer. Since these electroluminescent phosphor materials are field responsive and the brightness increases `fwith increased field intensity, this increased :electric field will cause the phosphor material to electroluminesce at that point which is aligned or contiguous with the excited photoconductor portion. 'This will cause the cathode-ray signal, for example, to be reproduced by the electroluminescing phosphor material. Specific examples of suitable electron-hombar-dment-conductive materials which may be excited by cathode rays are cadmium telluride, cadmium selenide,I cadmium sulde and anthracene.

Since many photoconductive materials which are excitable by cathode rays to vary in impedance are also excitable by visible light to vary in impedance,`it is sometimes `desirable to place a layer of light-shielding material between the phosphor 48 and the photoconductive layer 50 in order to prevent optical feedback from the phosphor to the photoconductive layer, which `optical ,feedback would, of course, tend to cause the phosphor layer i8 to lock-in and electroluminesce even when the excitation signal was removed. Where :a separate layer of lightshielding material is utilized, this layer 52 should be'of high electrical resistivity, and such a construction is shown in FIG. 6. If a layer of aluminum were to be rutilized as a light shielding means, for example, the conducting nature of this material would cause the entire phosphor layer 4S to electroluminesce whenever a small por-tion` of the photoconductive material 50 was rendered conducting, as this would have the effect of placing the photoconductor in series with the electroluminescent layer 48. As la specific example, a layer 52 of opaque plastic such as opaque polyvinyl` chloride may be used between the phosphor layer 43 and the photoconductive layer 50 in order to prevent optical feedback when the photoconductive layer is excited by the light which the phosphor material produces when excited :by an electric field. lt should be noted that anthracene is only very slightly excited by visible light. If anthracene is used as the photoconductive layer 50 and the phosphor electroluminesces to produce visible light, the shielding layer 52. may normally be dispensed with.

Under some conditions of operation, the light-shielding layer SZ -between the phosphor and the photoconductive layers may be dispensed with, even when the photoconductive 'material is excitable lby the radiations produced by the phosphor. For example, the alternating potentials of varying frequency may be interrupted between individual scansions so that they are .applied lfor the period the corresponding screen-excitational signal is simultaneously applied to the photoconductive lay-er 50. This will cause the electroluminescent phosphor to produce visible radiations which will in turn cause some optical feedback in the photoconductive l-ayer 50 and this will increase the rate at which the light builds iup in the electroluminescent layer 48. Before the next individual cathode-ray vlscansion, the exciting electric field for the electroluminescent phosphor is also removed and the screen will assume a quiescent status before it is again energized by the next scansion. `characteristics which will be present in such a construction may impair the contrast as well as the resolution of the generated signals, but this may not always be objectionable, Idepending upon the particular application. For many purposes, however, it is desirable to include the light-shielding layer 52 whenever the photoconductive material is excitable by the radiations which are generated The optical-feedback by the electroluminescent phosphor, in order to eliminate lock-in.` andso that Weak signals rarecontrasted and the resolutionofthe. signalsis as sharp as possible. 'I'his is perhaps moreimportant where the signals which are to bel displayed on the screen are to be amplified by the light-amplifying potentialities of the screen, since the excitationwof :the photocondnctive layer will then be dominated moreby the electroluminescence than` by the screenexcitation signal, with. resulting impairmentfof the signal contrast-and resolution..

T he inner electrode 46 should be electrically-conductive and tnansmissive to the incident signal excitation which is-impressed: thereupon to excite the photoconductive 1ayer'50'. In` the-case of excitation by cathode-ray scan- Ysions,.the'electrode 46 niay'be formed of aluminum which may -be deposited .by Well-known vacuumametallizing techniques. 'Ilhe cathode-ray tube 36 maybe fabricated by the usualtechniques except that the screen 4Z may be hermetically sealed to the. rest of the cathode-ray tube iat its periphery 54 by an adhesive such as the well-known epoxy resins;

Inthe embodiment shown in FIG. 6, the light-shielding layer 5Z1ntay also servesthe dual purpose of a layer of highidielectric material Ito prevent electric breakdown across the electrodes and to prevent optical feedback if the photoconductive layer is excitableby the radiations pnoduced-by the phosphor. Alternatively, the phosphor and. dielectricr material, which rnay be a suitahle high- -dielectric plastic material such as light-transmitting polyvinyl-chloride acetate, vfor example, may be admixed. The phosphor and admixed'dielectric maybe used in equial partsby Weight, .for example, although the-se proportions inlay be varied considerably. If the phosphor land dielectric..material lareadmixed, the phosphor-dielectric layer may have7 a thickness or about3 mils, for example, and if the phosphor is not admixed with the dielectric, it may have a thickness of .about 2 mils, for example. Such phosphor .and phosphor-dielectric constructions will normallybe .suitable for operation underl the applied voltages,

.Iasliereinafter specified. Of course, all of the material of the soreen 42 which is located between the Iouter electrode t4-andthe phosphor portion 48 of the screen should be tnansmissive for the radiations which .are generated by the phosphor-When it electroluminesces.

In order .for the phosphors to' display the different desired'colors, the excited portions of the photoeonductive layer should conduct for a period of at least one-half cycle oflthe. exciting electric field. This may be accomplished byv the proper selection `of photocon-ductors, for example, or by the proper selection ofthe phosphors which may be used tovexcite` the photoconductors, as described hereinafter, with particular regard to their `decay characteristics. 'Ihislnieans' that either the l aast portion Iof each oathode-nay. scansion may, be sacrificed or the exciting lield mu'stbe continuedfor la Ishort time after individual oathlode-ray scamsion is completed. Als-o, when using exciting electriciields of. very high frequencies in lorder to produce the differentoo-lors in. the phosphor, the decay characteristics for.. the-photooo-nductor .or exciting` phosphor lare a secondary consideration.

It may be desirable for some uses to construct the oathode-ray tu'be.36 in rtheusual fashion so that la layerlovf visible-light-producing phosphor material 56 is carried on the. endfofthe vtube and is Vscanned by the ycathode rays.- Such a constrnction. is shown in FIG. 7 and zinc silicatemanganese 'activated phosphor is suitable for this purpose.

y The visibleiinages which lare pnoducedby this phosphor 56 rniay be used to excite the viewing screen 42 which may be aixed .either to theinterior or to the exterior of the face of the-cathode-ray tube 36.' 4In such an embodiment the inner electrode 46 may also be tin oxide andthe photoeon'ductivematerial may becad-mium sulfide.

In FIG. 8 is illustrated Ian embodiment wherein the light signals which are produced yon the face of the cathode nay tube 36' are projected by means of a lens system 58 onto an enlarged screen 42a.. Such enembodiinent is construoted as indicatedV hereinbefore except that thevariable frequency source of alternating potentials is connected lacnoss the enlargedscreen 42a and .theiapplioation ofthe. potentials to the screen 42a is synehronizedwith the exei'tartion signals which 'are .imposed onthe photoeonduetive.I portion 50 of the screen 42a. If the photoconductiwe m'aterial is excitable byvisible light, it is desirable to shield the photozconductive material fnorn unwanted light by means of a shielding. enclosure y60. Of course, the inner electrode 46 should he transmissive for the scheen excitation signals and tin oxide is suitable for this purpose.

It may be desirable to. generate ultraviolet radiations by the cathode-nay scansions and phosphore which Iare exeit.-

able by cathoderays to produce ultraviolet light lane zinc.' pyrophosphate or cerium-activlated strontium orth'ophosphate, for example. In such an embodiment, allV of the vitreous or other material which is positioned between the phosphor and the photoconductive material should be. ultra-violet tnansmissive, such vitreous materials. being quartz or Vycor, for example. Anthraoene isl aphotoeonduetive material which is excitable by ultraviolet light and not by visible Ilight and in such an embodiment, the lightshielding enclosure 60 dan be dispensed with.

Alternatively, it may be desired to excite the phosphor vuhiohis coated onto the face of the cathode-ray ytube 36 to produce infrared radiation. This infrared radiation can then be projected onto theilarge viewing screen 42a. A. photooonductive material which is excitable by intraredl radiation and not' by visible light is cadmium telluride and' in such an embodiment, the light-shielding enclosure 60d can be dispensed with. Cathode-ray responsive phosphoreV which will generate infrared nadiations land which maybe: ooated lonto the face of the cathode-ray tube 36' are zinc sulphide activated by iron or |cadmium sulphide activated. by copper, for example.

ln FIG. 9 is shown an alternative embodiment of an. enlarged screen arrangement, -as shown in FIG. 8. This. 4alternative cmbodimentis identiealwith FIG. 8 exceptthat the lens system 58 as used for enlarging the screenexcitation signal, is replaced by la Schmidt-type spherical' mirroror rellector 62'. Such mirmrsiare Well knownand may be pressed from plastic or metal 4and rendered reflective for visible,` infrared or ultraviolet light byl vlacuuinsmetallizingl la thin' coating of aluminum over the. reflector surface'. Otherthan'this, the embodiment shown in FIG. 94 is similar'to the emhofdsifment shown in FIG. 8.V As is well known, the Schmidt mirror 62 maybe corrected 'for spherical Iaberration by an' additional glass-correcting. member 64, placed between the mirror 62' and the inner. electrode Li-of the screen' 42a'.

summarizing thev general operation of the foregoing. system, it will `beseen that'therefhas been provided a. transmitter arrangement wherein an object -eld is scanned 1na pluralityy of successive `field scansions corresponding.. to the primary color" eomp'on'ents' ofy the object field.. T hese scansions are converted into. a video signal. The video signal is'tnansmitted to' the receiver where it isA converted to successive individual screen-excitation signals 'which correspondto the successive li'eld soansions effected at the transmitter.` These successive screenexcitation signals may take the form of infrared images, ultraviolet images. visible light images, .or cathode-rayi scansione Vand4 thesesuccessive individual-screen-excitation `signals are projected in an incident fashion onto aw photoconductive material. This screen-excitationV signalr lowers `the impedance of that portion ofthe photoconductive material lwhere it, strikes, with the degree of` impedlance variation. normally increasing withv the intensity of the' excitation. signal.A This in turn allows thatportiom Y i color is synchronized with the application `of the color- `corresponding screen-excitation signal to the photoconductive portion of the screen. The signals are thus reproduced simultaneously in a plunality of individual colors since the eye blends together the rapidly-applied signals.

In operating the embodiments as illustrated, the voltages which are tapplied across the electrode 44 and 46 may be 500 volts, for example, although these volt-ages may be varied considerably depending upon the signal Ibrightness which is desired. Such `applied voltages normally 1vmill result in some degree of signal amplificatiom; that is, the signals which are reproduced in different colors will be brighter .than if a phosphor were to be excited by cathode-ray scansions alone, for example. lf it is not desired to amplify .the signals, the voltage which is applied across the electrodes may be reduced in an amount which will vary with the phosphor materials which are used, the type of photoconductive material `which is used and the `general construction'al `details of the screen 42. As a genenal rule, however, 100 volts applied across the electrodes will result in signal reproduction without amplification.

In the foregoing specifi-'c examples, a Ithree-color phosphor is disclosed which will electroluminesce in the yellow, .green and blue regions of the visible spectrum, when excited by `alternating potentials of different frequencies. t may be desired to produce red, green and blue signals instead of yellow, green and .blue signals. In this case a filter `66 may be placed -across the front of the viewing screen i2 and such an embodiment is shown in FIG. l0. This filter desirably outs out only those radiations having a wavelength of from about 5700v A.U. `to about 6100 A.U. The yellow 'color which is produced by the phosphor, as hereinbefore specified, is quite rich in red radiations and when the yellow radiations are filtered` out, the phosphor will be lgenerally red-emitting in nature. Suitable interference lters will meet these requirements, as is well known. In the event the filter arrangement is utilized to pass the red radiations and screen out most of the undesirable yellow radiations, it may be desirable to increase the brightness of the phosphor material when it is electrolfuminescing at the lower red-producing frequencies, in order that the lost radiations which lare screened by the lter may be made up, so that the phosphor will electrolumines at approximately the same brightness whenenengized at varying frequencies. Also,

accentuating certain colors is sometimes desirable. This increased brightness rat individu-al excitation frequencies may be `accomplished in several ways, such as increasing the voltage which the corresponding oscillator will apply across the electrolfuminescent cell. Alternately, an inductance may be placed in series `with the electroluminescent screen 42 and this arrangement is shown in FIG. iti. lnductances in series with electroluminescent cells are disclosed in ico-pending application of Willi Lehmann, S.N. 611,663, filed September-24, 1956, titled Electroluminescent Cell Combination, and owned by the present assignee and the desired value of such inductances may be readily Icaluculated fas :disclosed therein. As a specific example, for a cell having an area of 1G00 sq.

centimeters, (C=about 0.1 uf.) tan inductive reactance of 195 millihenries will produce a series resonance condition at about 360 cycles. This will result in increasing, at series resonance, the 'applied voltage across the cell by from 3 to 6 times that voltage which is supplied by the alternating potential source. This in turn will increase the brightness across the cell only at those frequencies at which resonance exists.

. ln the foregoing television-transmitter arrangementan entire object field has been scanned and thereafter repromay then be compositely presented. Also, in the fore-` tgoing receiver embodiment, the electron-beam scansions which comprise the individual signals may be interlaced, if desired.

The receiver system as described is adapted to receive and present synchronized signals. It should be clear that unsynchronized signals may be received and then synchronized by the receiver before presentation. In addition, the same object iield may be presented compositely in different forms and in different colors. For example, TV and radar pictures, radar PPI and infrared pictures or infrared and TV pictures of the same object field may be presented simultaneously and in different colors.

Depending on the decay characteristics of the photoconductor or the decay characteiisticsof a phosphor, the output of which may be used to excite the photoconductor, it may be desirable in some cases to augment the memory aspects of the exciting phosphor or the photoconductor, which memory aspects are introduced by the decay characteristics. This may be accomplished by utilizing the optical feedback lock-in characteristics which are present when the light-shielding means between the photoconductor and the electroluminescent phosphor are eliminated.l ln such an embodiment, the electroluxninescent voltages may be sufiiciently low during au individual scansion so that the applied signal will produce lock-in, but only a very weak light. After the scansion is complete, a strong exciting field may be applied for a period of at least one-half cycle of the exciting field, for example, to cause the impressed signal .to electroluminesce very brightly. All exciting Ifields may then be removed and the phosphor-photoconductor allowed to become quiescent before the next scansion. Other methods for achieving additional memory characteristics, where desired, are also available.

For some applications it may be desirable to eliminate all contrast between individual portions of individual signals and this may be achieved by utilizing the foregoing memory characteristics which are present during lockinY and continuing the strong exciting electric field after the cathode-ray scansion for a sufiicient time that contrast between individual portions of individual signals is eliminated.

It will be recognized that the objects of the invention have been achieved by providing a screen and receiver and receiver-transmitter arrangement wherein individual signals may be simultaneously presented in different colors. Also, a method for operating the receiver and the receiver-transmitter arrangement has been provided.

While in accordance with the patent statutes one bestknown embodiment of the invention has been illustrated and described in detail, it is to'be panticularly understood that the invention is not limited thereto or thereby.

'I claim:

l. A system for receiving different signals and simultaneously presenting such received signals in preselected different colors on a screen, comprising signal-converting means for converting said received signals into a plurality of individual screen-excitation signals corresponding to said received signals, a presentationscreen comprising two bounding and spaced electrodes having sandwiched therebetween electroluminescen-t phosphor material, a photoconductive layer also sandwiched between said bounding electrodes and adjacent one of said electrodes, said one electrode which is adjacent said photoconductive layer positioned to receive incident thereon said plurality of screen-excitation signals, said one electrode also being electrically conductive and transmissive` to'said screenexcitation signals, said plrotoconductive layer having the characteristic of being responsive to the said screenexcitation signals received by `said one electrode to decrease in impedance, `said phosphor characterized by capability-.of energization by preselected diiierent frequency electric tields to electroluminesce in a plurality of different `colors corresponding to said preselected different signal colors, said other bounding electrode formed of light-transmitting and electrically-conductive material, all of said screen material between said phosphor and said other electrode being light transmitting, alternating potential supply means for `supplying potentials of preselected different frequencies across said bounding electrodes to create therebetween electric elds which corre-- spond Yin frequency to those to which said phosphor material responds to electroluminesce in said different colors, and means for synchronizing the 'application of said individual screen-excitation signals to said one electrode and theY supply of said potential across said bounding electrodesso that'there issirnultaneously supplied across said bounding electrodes that alternating potential having such'.` frequency as can cause said phosphor to electroluminesce that color which is preselected for screen presentationV of that received signal which has corresponding thereto the individual screen-excitation signal which! is then applied to said one electrode, whereby said different received signalsy are simultaneously presented On'said screeninpreselected different colors.

2. A system forreceiving diierent signals and simultaneouslyjpresenting such reecived signals in preselected dilerent colors 'on a-scne'en, comprising signal-converting means for converting. said received signals into a pluralityv of individual screen-excitation signals correspondigtosaid'received signals, y,a presentation screen comprisingttwo b'oundingand spaced velectrodes having sandwiched therebetween electroluminescent phosphor material, a photoconductive layer also sandwiched between` said" bounding electrodesand adjacent one of saidelectrodes, high-resistance shielding` means between said phosphor and' said photoconductive layer when said photoconductive layer is excitable by visible light for preventing optical feedback from said phosphor to said photoconductive. layer, said one electrode which is adjacent saidl'photoconductive layer positioned to receive icidentthereon said plurality of screen-excitation signals, said' one electrode also being electrically conductive. andtransmissive` to said screen-excitation signals, said photoconductive layer having the characteristic of being'responsive kto the` said screen-excitation signals receive'd by' said'one electrode to decrease in impedance accordingto the intensity of said one electrode-received screen-excitation signals, lsaid phosphor characterized by capability of energization by preselected different frequen'cy electric ilelds to electroluminesce in a plurality of different colors corresponding to said preselected different signal colors, said lother bounding eelctrode formed of. light-transmitting and electrically-conductive material, allUofsaid screen material between said phosphor and said other. electrode .being light transmitting, alternating potentialsupply means. forasupplyingpotentials of preselected diifierent frequencies across said bounding electrodes .to create. therebetween. electric fields which. correspondin. frequency to..those to which said phosphor material. respondstoelectroluminesce in said different colorspand means for synchronizingthe application of said `indi-vidual screen-excitation signals to said one electrodefand thesupply of said potential across said boundingt electrodesyso that'therefis simultaneously supplied across saidbounding electrodes that alternating potential having such frequency ascan cause said phosphor to electroluminesce in that color which is preselected for screen `presentation-of that received signalY which has corresponding thereto the individual screen-excitation signal which: is then" applied to said one electrode, whereby said dilerent received signals are simultaneously presented ony said screen in-preselected different colors.

l3. A system for-receiving different signals and simultaneously presenting such received signals in preselected dierent'colors on asscreen, vcomprising signal-converting wiched between said bounding electrodes and adjacent one of said electrodes, a high-resistance shielding means between said phosphor and said photoconductive layer when said photoconductive layer is excitable by visible light for preventing optical feedback from said. phosphor to said photoconductive layer, said one electrode which is adjacent said photoconductive layer positioned to receive incident there-on'. said plurality of enlarged screenexcitation light signals, said one electrode also being electrically conductive and transmissiveto said enlarged' screen-excitation light signals, 4said photoconductive layer having the characteristic of .being responsive to the said enlarged'screen-excitation light signals received by said one electrode to decrease in impedance according to the intensity of said one electrode-received enlarged' screen-excitation light signals, said phosphor characterized by capability of energization by preselected different frequency electric fields to electroluminesce in a plurality of dierent colors corresponding to said preselected different signal colors, said other bounding electrode" formed of light-transmitting and electrically-conductive material, all of said -screen material between said phosphor and said-other electrode* being light transmitting," alternating potential supply means for supplying potentials of preselected dilferent frequencies across said bounding electrodesI to create therebetweenk electric iields which correspond in frequency to .those to-which said" phosphor material responds to electroluminescence said different colors, and means for synchronizing the application of said individual enlarged screen-excitationr light signalsv to said one electrode and the supply of said potential lacros said bounding electrodessso that there is simultaneously supplied across saidA bounding electrodes that alternating potential having such frequency as canV cause said phosphor to electroluminescein that color" which is preselected forV screen presentation of thatreccived signal which has corresponding thereto the indi-- vidual enlarged screen-excitation l-ightsignal which is' then applied to saidl one electrode,` whereby said dilerent received signals are simultaneously presented'on saidE screen in preselected different colors.

4. In a color television system: a transmitter which comprises scanning means for succesively scanning an lobject iield, color means associated. with said scanning means for successively presenting a plurality of reoccurring primary color components of said object yield to said scanning means during 'respective'iield -iscansion periods,

transmitter converting means associated' with said scan-Y ning means for converting said scansions into a video sign-al having components which correspond-to said suc-y cessive scansions; a receiver for converting said videoY signal into a color picture and comprising, 'video signal-- converting means for converting-said video-signal intoM a plurality of individual screen-excitation signals which correspond to the transmitter-scamion-componentsv of said video signal, a presentation screen comprising twobounding and spaced electrodes'havng'sandwiched therebetween electroluminescentphosphor material, a photoconductive layer also sandwiched betweensaid bounding electrodes and adjacent one of said electrodes, said one electrode which is adjacent said photoconductiveY layer positioned to receive incident thereon said plurality of screen-excitation signals, said one electrode also being electrically conductive and transmissive to. said screenexcitation signals, said photoconductive layer having the characteristic of beingl responsive` to the said screenexcitation signals received by said one electrode-to decrease in impedance according to the intensity of said electrode-received screen-excitation signals, said phosphor characterized by capability of energization by preselected different frequency electric fields to electroluminesce in a plurality of different colors corresponding to said preselected different signal colors, said other bounding electrode formed of light-transmitting and electrically-conductive material, all ofsaid screen material between said phosphor and said other electrode being light transmitting, alternating potential supply means for supplying potentials of preselected different frequencies across said bounding electrodes to create therebetween electric elds which Vcorrespond in frequency to those to which said phosphor material responds to electroluminesce in different colors, and means for synchronizing the application `of said individual screen-excitation signals to said one electrode and the supply of said potential across said bounding electrodes so that there is simultaneously supplied `across said bounding electrodes that alternating potential having such frequency as can cause said phosphor to electroluminesce in the color of that transmitterscansion-component of the received video signal which has corresponding thereto the individu-al screen-excitation signal which is then applied to said one electrode.

5. The method of reproducing individual signals in different colors in composite fashion -on :a screen comprising separate layers of photoconductor material and electrolurninescent phosphor material, which phosphor material layer when individually energized by alternating electric fields of predetermined intensities :and predetermined frequencies will display the ydifferent colors in which said signals are to be reproduced, which method comprises, individually exposing said photoconductive material llayer to each of said signals to decrease the impedance of exposed portions of said photoconductive material layer, and separately applying in synchronized fashion each of said predetermined electric -fields :across said screen phosphor and photoconductive material layers so that the individual exposure of any `one of said signals onto said photoconducti-ve material layer occurs simultaneous with the application yacross said phosphor and photoconductive material layers of that predetermined electric field `Which produces electroluminescent emission tof the color in which the signal 'then exposed onto said photoconductive layer is to be displayed.

6. The method of reproducing individual signals in different colors in composite fashion on a screen comprising separate laye-rs of photoconductofr material and electroluminescent phosphor material, which phosphor material layer when individually energized by alternating electric fields of predetermined intensi-ties and predetermined different frequencies will display the different colors in which said signals are to be reproduced, which method comprises, sequentially exposing said photoconductive material layer to each of said signals to decrease the impedance of signal-exposed portions of said photoconductive material layer, and sequentially applying in synchronized fashion each of said predetermined alternating electric fields across said screen phosphor and photoconductive material layers so that the exposure of any one of said signals onto said photoconductive material layer occurs simultaneous With the application across said phosphor and photoconductive material layers of that predetermined electric field which produces electroluminescent emission of the color in which fthe signal then exposed onto said photoconductive material layer is to `be disp-layed.

7. The method of reproducing individual signals in different colors in composite fashion on a screen comprising separate 'layers of photoconductor material 'and electroluminescent phosphor material, which phosphor material t layer when .individually energized by alternating electric fields of predetermined intensities and predetermined different frequencies Will display the different colors in which said signals are to he reproduced, which method comprises, individually 'and sequentially exposing said photoconductive material layer to each of said signals to decrease the impedance of exposed portions of said photoconductive material layer i-n an amount corresponding to the intensity of said signals, an-d individually ,and sequentially applying in synchronized fashion each of said predetermined alternating electric fields across said screen phosphor and photoconductive material layers so that the exposure Iof any one of said signals on to said photoconductive material layer occurs simultaneous with the application across said phosphor and photoconductive material layers of that predetermined electric iield which produces electroluminescent emission lof the color in which the signal then exposed onto said photoconductive material layer is to be displayed.

References Cited in the le of this patent UNITED STATES PATENTS 2,728,815 Kalf-aim Dec. 27, 1955 2,773,216 Edmonds Dec. 4, 1956 2,780,731 Miller Feb. 5, 1957 2,792,447 Kazan May 14, 1957 2,858,363 Kazan Oct. 2,8, 1958 2,861,206 Fiore et ral. Nov. 18, 1958 2,881,353 Michlin Apr. 7, y1959 2,892,095 Orthuber et @al June 23, l1959 2,900,555 Schneeberger Aug. 18, 1959 2,928,980 Williams Mar. 15, 1960 FOREIGN PATENTS 157,101 Australia June 16, 1954 OTHER REFERENCES," Proceedings I.R.E., December 1955, page 1918. 

5. THE METHOD OF REPRODUCING INDIVIDUAL SIGNALS IN DIFFERENT COLORS IN COMPOSITE FASHION ON A SCREEN COMPRISING SEPARATE LAYERS OF PHOTOCONDUCTOR MATERIAL AND ELECTROLUMINESCENT PHOSPHIOR MATERIAL, WHICH PHOSPHOR MATERIAL LAYER WHEN INDIVIDUALLY ENERGIZED BY ALTERNATING ELECTRIFIELDS OF PREDETERMIND INTENSITIES AND PREDETERMINED FREQUENCIES WILL DISPLAY THE DIFFERENT COLORS IN WHCIH SAID SIGNALS ARE TO BE REPRODUCED, WHICH METHOD COMPRISES, INDIVIAUALLY EXPOSING SAID PHOTOCONDUCTIVE MATERIAL LAYER TO EACH OF SAID SIGNALS TO DECREASE THE IMPEDANCE OF EXPOSED PORTIONS OF SAID PHOTOCONDUCTIVE MATERIAL LAYER, 